In a known plaintext attack, the cryptanalyst has knowledge of which of the following?

A.
the ciphertext and the key

B.
the plaintext and the secret key

C.
both the plaintext and the associated ciphertext of several messages

D.
the plaintext and the algorithm

Explanation:
Cryptanalysis is the act of obtaining the plaintext or key from the ciphertext. Cryptanalysis is used to obtain
valuable information and to pass on altered or fake messages in order to deceive the original intended
recipient. This attempt at “cracking” the cipher is also known as an attack.
In a Known Plaintext attack, the attacker has both the plaintext and the associated ciphertext of several
messages.
Incorrect Answers:A: In a known plaintext attack, the attacker does not have the key.
B: In a known plaintext attack, the attacker does not have the secret key.
D: In a known plaintext attack, the attacker does not have the algorithm.
Krutz, Ronald L. and Russel Dean Vines, The CISSP Prep Guide: Mastering the Ten Domains of Computer
Security, John Wiley & Sons, New York, 2001, p. 154